Photoacoustic and ultrasonic endoscopy system including a coaxially configured optical and electromagnetic rotary waveguide assembly and implementation method thereof

ABSTRACT

A photoacoustic-ultrasonic dual-mode endoscope includes: a probe and a probe driving unit, wherein the probe includes: a coaxially configured optical and electromagnetic rotary waveguide assembly including an optical fiber, the optical fiber including a core and a cladding, and a conductive path coaxially arranged with the optical fiber; a scanning tip located at an end of the coaxially configured optical and electromagnetic rotary waveguide assembly and configured to deliver a laser beam to an object to be examined and detect a photoacoustic signal and an ultrasonic signal generated from the object to be examined; and a plastic catheter surrounding outer surfaces of the coaxially configured optical and electromagnetic rotary waveguide assembly and the scanning tip, wherein the conductive path includes: a first conductive path including a portion coaxially arranged with the optical fiber; and a second conductive path including a portion coaxially arranged with the optical fiber and insulated from the first conductive path.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of Korean Patent Application No.10-2016-0107773, filed on Aug. 24, 2016, in the Korean IntellectualProperty Office, the disclosure of which is incorporated herein in itsentirety by reference.

BACKGROUND 1. Field

One or more of the embodiments described in the present disclosurerelate to a medical tomographic endoscopic apparatus that has a long andslender probe shape, like the current endoscopic ultrasound (EUS) probesutilized in clinics, wherein the endoscopic apparatus is inserted intothe object to be examined and provides a tomographic image of theinterior thereof. The key feature of the proposed endoscopic system isthe ability to provide both a high-quality photoacoustic image and atypical ultrasonic endoscopic image based on the improved probeflexibility and rotational uniformity compared to existing photoacousticendoscopic systems. The inventive concept of the present disclosure maybe applied to various medical imaging applications, such as thediagnosis of a digestive disease or cardiovascular disease.

2. Description of the Related Art

The present disclosure relates to a range of tomographic endoscopicsystems that can provide cross-sectional or volumetric images of targettissue according to the general principle of photoacoustic endoscopy(PAE) and EUS by consolidating the relevant functions in a singledevice. The proposed endoscopic systems are intended to be used for suchmedical procedures as the diagnosis of a digestive disease orcardiovascular disease by using a method similar to that of an EUSmini-probe or an intravascular ultrasound (IVUS) catheter probe, both ofwhich are currently utilized in clinics.

The general principle of EUS is already well known, well established,and currently being utilized. However, PAE refers to the noveltomographic endoscopic technique that embodies the photoacoustic imagingtechnique in a small probe. In an illustrative imaging procedure, aprobe with a small diameter is inserted into an object to be examined.Electromagnetic waves with a very short pulse width (usually less than 1μs) are instantly applied to the region of interest to generate acousticwaves, which are typically referred to as photoacoustic waves, and atomographic image of the interior of the biological tissue is producedby obtaining (i.e., scanning) the generated photoacoustic signals overthe region of interest.

Although the photoacoustic effect through which electromagnetic wavesare applied to a target object and converted into acoustic waves hasbeen known since the 1880s, it was not until the early of 1990s that thefirst photoacoustic image was actually obtained from real biologicaltissue based on the photoacoustic effect. At that time, the advent ofcommercial pulsed-light sources, such as the Q-switched laser, played acrucial role in the breakthrough; from then on, various types ofphotoacoustic imaging systems have been developed with a greater rangeof medical applicability. In general, a technique that can provide atomographic image of the interior of biological tissue based on thephotoacoustic effect is referred to as photoacoustic imaging (PAI) orphotoacoustic tomography (PAT) in a broader sense.

The reason that PAT is currently in the medical imaging spotlight isbecause it is capable of providing a new type of medically useful imageinformation that is not possible with conventional medical imagingtechniques, such as magnetic resonance imaging, X-ray computedtomography, positron emission tomography, and ultrasound imaging. Also,it is widely accepted that PAT is very superior in terms of the imagingdepth, spatial resolution, imaging speed, and safety, all of which arecritical factors for real clinical use. In short, the present disclosurerelates to the endoscopic application of PAT, and it is intended toprovide a description of the apparatus, the operation of the apparatus,and a method for implementing the apparatus that may solve the problemsrelated to existing PAE systems.

Like more well-known or more general PAT systems (that are not limitedto endoscopy), a PAE system also requires three core system elements: alight source that generates an electromagnetic pulse, an imaging probethat approaches an object to be examined and acquires a series ofphotoacoustic signals, and a data processor and displayer that processthe acquired photoacoustic signals and provide the processedphotoacoustic image to a user. However, the most important anddistinguishable technical requirement for the specific application ofendoscopy is an imaging probe with a very small or slender and longform.

After the first conceptual suggestion of PAE by Oraevsky et al. in 1997as described in Prior Document 5, in which the imaging probe wasreferred to as optoacoustic endoscope (OAE), a number of PAE probes weredeveloped to address such technical requirements as “probeminiaturization” and “specifying a device configuration or operationprinciple for endoscopy.” However, no commercially successful orclinically applicable PAE system that satisfies both of the technicalrequirements has been developed yet due to many underlying technicalchallenges. The most well-known and toughest challenge is that tosuccessfully create a working PAE probe, all the optical and acousticelements should be effectively integrated and arranged in a small andrestricted space; an adequate scanning mechanism, through which atomographic image can be produced, should also be developed andintegrated into the device. Accordingly, the main purpose of the presentdisclosure is to provide an advanced PAE system concept that may allowan imaging probe to be inserted into the living object to be examinedand provide a photoacoustic signal to obtain an image more effectivelythan in prior attempts.

Although there is a clear difference between the principles of PAE andEUS, in which a PAE image is produced through the unique energytransduction mechanism that converts pulsed electromagnetic waves intoacoustic waves, PAE is still very closely related to conventional EUS.This is because all of the signals required to produce a PAE image areacquired by means of acoustic waves. This means that, in some respects,a PAE device can be understood as a device in which the functions thatguide and emit laser light or electromagnetic waves are added to thetypical system composition of a conventional EUS device. Due to thesesystem characteristics, most PAE systems may be able to provide both aphotoacoustic and a typical ultrasound image.

Hence, regarding methods of ultrasound signal detection other than thosethat deliver and emit electromagnetic waves (e.g., a laser beam ingeneral) to an object to be examined, any of the single-elementultrasonic transducer-based mechanical scanning mechanism or arraytransducer-based electronic scanning mechanism currently being utilizedin clinical EUS instruments may also be utilized in a PAE probe. Theadvantages and disadvantages of the mechanical and the electronicscanning mechanisms will be briefly explained in the following.

First, the main advantage of the electronic scanning mechanism is thatall of the one-dimensional signals (i.e., A-lines) needed to produce atwo-dimensional (2D) or three-dimensional (3D) tomographic image may besimultaneously obtained through the plurality of detection channelsformed in an array transducer by using a single shot of anelectromagnetic pulse (e.g., laser pulse). This means that, withoutmaking any changes to the sensor or probe position, a tomographic imagecovering a certain range of the target region may be acquired at onetime after just one laser pulse firing. However, the main drawback ofthe electronic scanning mechanism is that, since it is relatively moredifficult to reduce the size of the related endoscopic probe than thatof the mechanical scanning mechanism, such problems as crosstalk orsignal interference between channels may occur; the costs ofimplementing the system may also be high. Due to the aforementionedproblems with an array transducer, in the current EUS technologyutilized in clinics, the electronic scanning mechanism is mostly adoptedto such EUS devices that are manufactured for the diagnosis of digestivediseases, for which high-level miniaturization is unnecessary (ofcourse, an EUS instrument does not require a laser pulse guiding andemitting function).

In contrast, the mechanical scanning mechanism differs from theelectronic scanning mechanism in the following ways. First, its majordrawback is that, since a single-element ultrasonic transducer that canreceive the signals bounced back only from the aiming direction of thetransducer surface is mounted on the scanning tip of an endoscopicprobe, in order to obtain a 2D or 3D image, a series of processes thatemit a laser pulse and then detect the generated photoacoustic wavesshould be repeatedly performed by changing the physical position or theaiming direction of the ultrasonic transducer (e.g., rotational scanningin general). However, the mechanical scanning mechanism also hasadvantages. Since the space occupied by the single transducer is not solarge, forming a very small or slender-shaped probe may be possible. Thecosts of developing and creating the instrument are also relatively low.Accordingly, in the current EUS technology utilized in clinics, themechanical scanning mechanism is mostly applied to ultra-smallendoscopic instruments with probe diameters ranging from ˜1 mm to ˜3 mm,such as IVUS catheter probes manufactured for introduction into bloodvessels or EUS mini-probes manufactured to be inserted into theinstrument channels or the accessory channels of a video endoscope.

Due to the aforementioned advantages and disadvantages, various PAEsystems with the adoption of one of the two ultrasound signal detectionmechanisms have been suggested so far. Among them, representativeexamples of prior technologies using a single-element ultrasonictransducer-based mechanical scanning mechanism, which is actually thesame mechanism that the present disclosure has also adopted as atechnical basis, include Prior Document 1 (US Patent ApplicationPublication No. 2011-0021924), Prior Document 2 (US Patent ApplicationPublication No. 2011-0275890), Prior Document 3 (Journal of BiomedicalOptics 19(6), 066001(2014)), and Prior Document 4 (PLOS ONE 9(3), e92463(2014)).

The endoscopic systems disclosed in the four prior documents mentionedabove use a mechanical scanning mechanism in which a light illuminationunit coupled to the end of an optical fiber to deliver laser light and asingle-element ultrasonic transducer to detect generated photoacousticwaves are closely placed at the scanning tip of a probe; signal data toproduce a photoacoustic image is acquired through the predeterminedrotational motion of the scanning tip. However, the methods of placingthe optical fiber, the light illumination unit, and the ultrasonictransducer, as well as a detailed scanning mechanism to obtain an imagebased on the aforementioned system configuration differ among theendoscopic systems disclosed in the prior documents. These differenceswill be briefly reviewed and discussed.

First, in the PAE probe disclosed in Prior Document 1, a single-elementultrasonic transducer is placed at the scanning tip, like an existingultrasound-based IVUS catheter probe. The mechanical torque required forthe rotational motion of the scanning tip is transmitted from theproximal part of the system to the scanning tip through a mechanicalcomponent called a “torque coil” (in the drawing, it seems that a realcommercial IVUS catheter or its equivalent is directly placed at thecentral part of the endoscopic probe to realize the mentioned parts andfunction). However, the most notable feature of the endoscopic probe isthat a plurality of optical fibers to deliver laser light are placed atpredetermined intervals around the IVUS catheter or its equivalent sothat the required process for photoacoustic imaging can be performed. Inthis configuration, the main advantage is that the optical fibers areplaced around the catheter, which is typically a plastic tube, and maybe statically connected to the proximal part of the endoscopic probe,whereas the ultrasonic transducer is located at the central part of theendoscopic probe and rotates inside the plastic catheter. However, themain drawback of the endoscopic configuration may be that, since themultiple optical fibers are placed around the IVUS catheter, theflexibility of the probe may significantly deteriorate. The intensity ofthe laser light irradiated to the target tissue may also not be uniformover the 360-degree rotational angle.

In contrast, the endoscopic systems disclosed in Prior Documents 2through 4 do not have the above problems and have features as follows.

The most prominent feature and the biggest advantage of the endoscopicsystem disclosed in Prior Document 2 is a scanning mirror that canreflect both laser light and acoustic waves; it can also physicallyrotate and is employed inside the scanning head of the endoscopic probe.Both the signal wire of the transducer and the optical fiber thatdelivers the laser light can therefore be statically connected to theproximal part of the endoscopic probe along the probe body. However, theendoscopic system also has problematic issues. Since an actuator fordriving the scanning mirror has to be mounted inside the scanning headof the probe, the flexibility of the distal section may be greatlyreduced (in fact, this reduction in the flexibility runs counter to theoriginal objective of such a mini-probe and may cause many problems whenthe endoscopic system is used in real clinics).

On the other hand, the endoscopic system disclosed in Prior Document 3,which may be regarded as an alternative embodiment derived from thebasic concept of Prior Document 2, differs in the following ways. Only asingle strand of optical fiber placed inside a torque coil along thecentral axis of the endoscopic probe performs a rotational scanningalong with a scanning mirror, whereas an ultrasonic transducer and itssignal wire are still statically connected from the scanning head to theproximal part of the endoscopic probe along the outer surface of aplastic tube or catheter. So, when the endoscopic system conceptdescribed in Prior Document 3 is used, the total length of the rigiddistal section of the endoscopic probe may be formed with a much shorterlength than that of the endoscopic system described in Prior Document 2.However, the endoscopic system in Prior Document 3 has the problem thata portion of the angular field-of-view is inevitably blocked by thesignal wire of the transducer (i.e., a blind spot is formed in theimage), and the probe has an asymmetrical structure due to the signalwire. Thus, the rotation speed of the scanning tip may not be uniformwhen the rotational scanning is performed with the probe bent into acomplex shape.

In these respects, the endoscopic system described in Prior Document 4displays many interesting system features that may be able to solve mostof the above problems. First, regarding structure, a light illuminationunit and an ultrasonic transducer element with a small size are placedtogether in the scanning tip which is formed at the distal end of theprobe. A signal wire to transmit electrical signals from the transduceras well as an optical fiber to deliver a laser beam to the lightillumination unit are installed in a flexible and tubular coil, which isreferred to as a flexible shaft or a torque coil; these perform arotational scanning along with the scanning tip. In this case, thetorque coil that encloses the signal wire and the optical fiber acts asthe key mechanically-rotating agent that transmits the mechanical torquesupplied from a proximal part of the endoscopic probe to the scanningtip (in the endoscopy field, the related operational principle isreferred to as a torque coil-based proximal actuation mechanism).

In fact, a method of implementing a PAE probe like the endoscopic systemdescribed in Prior Document 4, in which a single-element ultrasonictransducer and a single strand of optical fiber are employed and thesignal wire of the transducer and the optical fiber are placed veryclosely in parallel by forming a long probe structure, was firstsuggested in Prior Document 5 published in 1997. Afterward, the same orsimilar design concepts with minor variations have been continuouslyapplied to later PAE systems (e.g., Prior Documents 6, 7, and 8). Also,a method of transmitting mechanical torque from the proximal part of anendoscopic system to a scanning tip via a torque coil, thus performing arotational scanning, has also been continuously applied to many EUSmini-probes or endoscopic optical coherence tomography (OCT) probes(e.g., Prior Documents 9 and 10) for more than twenty years.

In this regard, a PAE system that employs a torque coil-based proximalactuation mechanism may be understood as a photoacoustic version of anEUS mini-probe because all current clinical EUS mini-probes are alsooperated based on the same scanning mechanism. However, the biggestdifference between the PAE probe and the EUS mini-probe is that anoptical fiber to deliver laser light is additionally required for thePAE imaging function, and it should be properly installed somewhereinside a torque coil. In addition, another very important systemcomponent capable of transmitting and/or receiving both laser light andtransducer electrical signals without interference should be embodiedeffectively at the proximal part of a PAE probe. In other words, if thetorque coil-based proximal actuation mechanism is adopted for a PAEsystem, as in the case of Prior Document 4, the development of a rotaryoptical and electromagnetic coupling unit (or the like) with a morecomplicated structure than that of an existing EUS mini-probe would beone of the key tasks.

Nonetheless, the achievement of a PAE system based on the aforementionedtorque coil-based proximal actuation mechanism is still regarded as oneof the ultimate goals in the related field because the mechanism has akey advantage: the entire catheter section of an endoscopic probe may beformed with much greater flexibility than in the endoscopic systemsdescribed in Prior Documents 1 through 3. Besides, the mechanism alsoenables full 360-degree rotational scanning without including any blindspot in an acquired image.

As the probe flexibility is a primary consideration in designing an EUSmini-probe with the main objective of being inserted into the instrumentchannel of a video endoscope or an IVUS catheter probe with the mainobjective of diagnosing the interior of a blood vessel that isphysically very weak, so far a number of PAE systems (e.g., in Priordocuments 4 and 8) have been developed that are based not only on thescanning mechanism of the EUS mini-probe or the IVUS catheter probe, butalso on the application objects and the probe types similar to the EUSmini-probe or the IVUS catheter probe, which actually use the sametorque coil-based proximal actuation mechanism. However, none of theprior documents have described a successfully achieved PAE system withthe torque coil-based proximal actuation mechanism.

PRIOR DOCUMENTS Patent Documents

Prior Document 1: US Patent Application Publication No. 2011-0021924(Jan. 27, 2011)

Prior Document 2: US Patent Application Publication No. 2011-0275890(Nov. 10, 2011)

Prior Document 7: US Patent Application Publication No. 2011-0098572(Apr. 28, 2011)

Prior Document 10: U.S. Pat. No. 6,134,003 (Oct. 17, 2000)

Non-Patent Documents

Prior Document 3: J M Yang, et al., “Catheter based photoacousticendoscope”, Journal of Biomedical Optics 19(6), 066001 (2014)

Prior Document 4: X Bai, et al., “Intravascular optical-resolutionphotoacoustic tomography with a 1.1 mm diameter catheter”, PLOS ONE9(3), e92463 (2014)

Prior Document 5: Oraevsky, et al., Proc. SPIE, 2979, 59 (1997)

Prior Document 6: Viator, et al., “Design and testing of an endoscopicphotoacoustic probe for determination of treatment depth afterphotodynamic therapy”, Proc. SPIE 4256, 16-27 (2001)

Prior Document 8: Da Xing, et al., “Characterization of lipid-richaortic plaques by intravascular photoacoustic tomography”, Journal ofthe American college of cardiology 64(4), 385-390 (2014)

Prior Document 9: G. J. Tearney, et al., “Scanning single-mode fiberoptic catheter-endoscope for optical coherence tomography”, OpticsLetters 21(7), 543-545 (1996)

Prior Document 11: J M Yang, et al., “Simultaneous functionalphotoacoustic and ultrasonic endoscopy of internal organs in vivo,”Nature Medicine 18(8), 1297 (2012).

SUMMARY

Existing PAE systems (e.g., in Prior Documents 4, 7, and 8) using atorque coil-based proximal actuation mechanism have problems in that,since the optical fiber and the signal wire are simply arranged in aparallel structure inside a torque coil, mechanical torque cannot beuniformly transmitted from the proximal part to the scanning tip of theprobe. The problem becomes even worse when a rotational scanning isperformed in conditions under which the endoscopic probe is insertedinto a narrow path with a high curvature. Since the optical fiber andthe signal wire are not configured with rotational symmetry around thecentral axis of the torque coil in existing PAE probes, mechanicaltorque cannot be uniformly transmitted from the proximal part to thescanning tip of an endoscopic probe when the probe is bent with a highcurvature, thereby decreasing the quality of the image.

When the proximal part of the torque coil rotates by a specific anglebut the scanning tip at the opposite end fails to rotate by the sameangle, and when the difference varies greatly with various probecurvature, the reliability of the obtained image is seriously reducedand it is also impossible to produce a reliable 3D image based on theacquired series of 2D cross-sectional images. Accordingly, in therelated art, avoiding the non-uniform rotational motion of the scanningtip is regarded as a very important issue, with the use of the technicalterm “non-uniform rotational distortion (NURD)”. However, no prior PAEsystems have satisfactorily solved the two aforementioned technicalproblems, i.e., the flexibility of the entire probe section and therotational uniformity of the scanning tip.

In addition to the major problems described above, since the endoscopicsystem disclosed in Prior Document 4 using a torque coil-based proximalactuation mechanism and other PAE systems that are similar do notinclude such system element as a plastic catheter or sheath as aprotective cover for the entire endoscopic probe, which is commonlyequipped in EUS mini-probes utilized for the diagnosis of digestivediseases and IVUS catheter probes utilized for the diagnosis ofcardiovascular diseases, no specific structures or methods also havebeen provided for isolating the scanning tip from an object to beexamined and thus protecting the object when the scanning tip of theprobe physically rotates. In addition to the previously mentioned basicfunctions, covering the entire scanning tip and the torque coil with aplastic catheter has another important technical aspect. Like existingEUS mini-probes developed to be inserted into the instrument channel ofa video endoscope, in a PAE probe developed to be used in a similarmanner, an appropriate acoustic matching liquid medium has to be filledinside the probe, and the probe has to be permanently sealed. However,prior PAE systems (in Prior Documents 4 and 8) fail to provide aspecific structure or method for covering the entire scanning tip andthe torque coil with a plastic catheter.

In other words, in a PAE system using a torque coil-based proximalactuation mechanism, a method of appropriately sealing the entirescanning tip and the entire torque coil section that physically rotateinside a plastic catheter and effectively implementing a rotary opticaland electromagnetic coupler at the proximal part of the probe is veryimportant. However, the method is not specifically disclosed in theprior documents.

Additional aspects will be set forth in part in the description whichfollows and, in part, will be apparent from the description, or may belearned by practice of the presented embodiments.

According to one or more embodiments, a photoacoustic-ultrasonic (i.e.dual-mode) endoscope includes a probe and a probe driving unit, whereinthe probe includes: a coaxially configured optical and electromagneticrotary waveguide assembly including an optical fiber and a conductivepath, wherein the optical fiber includes a core and a cladding, and theconductive path is coaxially arranged with the optical fiber; a scanningtip located at an end of the coaxially configured optical andelectromagnetic rotary waveguide assembly and configured to deliver alaser beam to an object to be examined and detect a photoacoustic signaland an ultrasonic signal generated from the object to be examined; and aplastic catheter surrounding outer surfaces of the coaxially configuredoptical and electromagnetic rotary waveguide assembly and the scanningtip, wherein the conductive path includes: a first conductive pathincluding a portion coaxially arranged with the optical fiber; and asecond conductive path including a portion coaxially arranged with theoptical fiber and insulated from the first conductive path.

The first conductive path may surround the optical fiber, and the secondconductive path may be coaxially arranged with the first conductive pathand surround the first conductive path.

At least one from among the first conductive path and the secondconductive path may have a tubular shape.

At least one from among the first conductive path and the secondconductive path may include a torque coil set formed as a coil outsidethe optical fiber.

Each of the first conductive path and the second conductive path maysurround at least a portion of the optical fiber.

The coaxially configured optical and electromagnetic rotary waveguideassembly may include an insulating coating layer between the firstconductive path and the second conductive path.

The cladding may include a first cladding configured to propagate lightwaves and a second cladding surrounding the first cladding.

According to one or more embodiments, a photoacoustic-ultrasonic (i.e.dual-mode) endoscope includes a probe and a probe driving unit, whereinthe probe includes: a coaxially configured optical and electromagneticrotary waveguide assembly including an optical fiber and a conductivepath, wherein the optical fiber includes a core and a cladding, and theconductive path is coaxially arranged with the optical fiber; a scanningtip located at an end of the coaxially configured optical andelectromagnetic rotary waveguide assembly and configured to deliver alaser beam to an object to be examined and detect a photoacoustic signaland an ultrasonic signal generated from the object to be examined; aplastic catheter surrounding outer surfaces of the coaxially configuredoptical and electromagnetic rotary waveguide assembly and the scanningtip; and a rotary transformer electrically connected to the conductivepath, and the probe driving unit includes: an optical inputterconfigured to deliver light energy to the optical fiber, wherein theoptical fiber rotates; and an ultrasonic pulser-receiver electricallyconnected to the rotary transformer.

The rotary transformer may include: a primary coil unit electricallyconnected to the conductive path; and a secondary coil unit facing theprimary coil unit and electrically connected to the ultrasonicpulser-receiver.

The photoacoustic-ultrasonic (i.e. dual-mode) endoscope may furtherinclude a mesh reinforcement inside the plastic catheter.

The probe may further include an injection port.

The photoacoustic-ultrasonic (i.e. dual-mode) endoscope may furtherinclude: a guiding catheter surrounding the plastic catheter andincluding a guiding catheter injection port; and a guiding wire insertedinto the guiding catheter injection port.

The photoacoustic-ultrasonic endoscope may further include a lightsource for optical coherence tomography (OCT), wherein the light sourceis configured to supply light waves for OCT to the optical fiber.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects will become apparent and more readilyappreciated from the following description of the embodiments, taken inconjunction with the accompanying drawings in which:

FIG. 1 is a view illustrating a configuration of aphotoacoustic-ultrasonic endoscope including a coaxially configuredoptical and electromagnetic rotary waveguide assembly and a rotaryoptical and electromagnetic coupler, according to an embodiment;

FIG. 2 is a cross-sectional view taken along line II-II′ of FIG. 1;

FIG. 3 is a view illustrating a configuration of a coaxially configuredoptical and electromagnetic rotary waveguide assembly in aphotoacoustic-ultrasonic endoscope, according to another embodiment;

FIG. 4 is a perspective view illustrating a detailed configuration of aportion A of the coaxially configured optical and electromagnetic rotarywaveguide assembly of FIG. 3;

FIG. 5 is a photo showing a real embodiment of the coaxially configuredoptical and electromagnetic rotary waveguide assembly according to thestructure shown in FIG. 4;

FIG. 6 shows a perspective view and a cross-sectional view illustratinga configuration of the coaxially configured optical and electromagneticrotary waveguide assembly according to an embodiment;

FIG. 7 shows a perspective view and a cross-sectional view illustratinga configuration of the coaxially configured optical and electromagneticrotary waveguide assembly according to another embodiment;

FIG. 8 shows a perspective view and a cross-sectional view of thecoaxially configured optical and electromagnetic rotary waveguideassembly including a double-clad optical fiber according to anembodiment;

FIG. 9 is a view illustrating a structure and a configuration of ametal-mesh embedded plastic catheter, according to an embodiment;

FIG. 10 is a view for explaining a shape and a structure of the plasticcatheter modified to be used for intravascular endoscopy and a method ofinjecting a liquid medium, according to an embodiment;

FIG. 11 is a view for explaining a configuration of the plastic catheterto be used with a guiding wire, and a process of performing a pullbackscanning, according to an embodiment;

FIG. 12 is a view illustrating configurations of a proximal part and adriving unit, according to another embodiment;

FIG. 13 is a conceptual diagram illustrating a photoacoustic-ultrasonicendoscopic probe, a probe driving unit, and a system console for drivingand controlling the probe and the probe driving unit; and

FIG. 14 is a conceptual diagram illustrating system elements forimplementing a photoacoustic-ultrasonic-optical coherence tomography(OCT) triple imaging mode, and a connection relationship among thesystem elements.

DETAILED DESCRIPTION

The present disclosure may include various embodiments andmodifications, and embodiments thereof will be illustrated in thedrawings and will be described herein in detail. The advantages andfeatures of the present disclosure and methods of achieving theadvantages and features will be described more fully with reference tothe accompanying drawings, in which embodiments are shown. The presentdisclosure may, however, be embodied in many different forms and shouldnot be construed as being limited to the embodiments set forth herein.

Reference will now be made in detail to embodiments, examples of whichare illustrated in the accompanying drawings. In the drawings, the sameelements are denoted by the same reference numerals, and a repeatedexplanation thereof will not be given.

It will be understood that although the terms “first”, “second”, etc.may be used herein to describe various elements, these elements shouldnot be limited by these terms. These elements are only used todistinguish one element from another.

As used herein, the singular forms “a”, “an”, and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise.

It will be further understood that the terms “comprises” and/or“comprising” used herein specify the presence of stated features orcomponents, but do not preclude the presence or addition of one or moreother features or components.

It will be understood that when an element is referred to as being“connected to” another element, it may be directly or indirectlyconnected to the other element. That is, for example, interveningelements may be present.

As used herein, the term “and/or” includes any and all combinations ofone or more of the associated listed items. Expressions such as “atleast one of,” when preceding a list of elements, modify the entire listof elements and do not modify the individual elements of the list.

FIG. 1 is a view illustrating a configuration of aphotoacoustic-ultrasonic endoscope including a coaxially configuredoptical and electromagnetic rotary waveguide assembly and a rotaryoptical and electromagnetic coupler, according to an embodiment;

Referring to FIG. 1, the photoacoustic-ultrasonic endoscope (alsoreferred to as a PAE-EUS system) according to an embodiment includes animaging probe 200 (hereinafter, the imaging probe is referred to as aPAE-EUS probe) and a probe driving unit 100. The PAE-EUS probe 200includes a coaxially configured optical and electromagnetic rotarywaveguide assembly 240 including an optical fiber 241 including a core241Co (see FIG. 7) and a cladding 241Cd (see FIG. 7), a conductive pathCP coaxially arranged with the optical fiber 241, a scanning tip 250located at one end (e.g., the distal end) of the coaxially configuredoptical and electromagnetic rotary waveguide assembly 240 and configuredto deliver a laser beam to an object to be examined and detect aphotoacoustic signal and an ultrasonic signal generated from the objectto be examined, and a plastic catheter 220 surrounding outer surfaces ofthe coaxially configured optical and electromagnetic rotary waveguideassembly 240 and the scanning tip 250. The conductive path CP includes afirst conductive path 242 including a portion coaxially arranged withthe optical fiber 241 and a second conductive path 243 including aportion coaxially arranged with the optical fiber 241 and insulated fromthe first conductive path 242.

In order to solve the problems of the prior arts, the present disclosureprovides the PAE-EUS probe 200 including the coaxially configuredoptical and electromagnetic rotary waveguide assembly (hereinafter, itis referred to as the waveguide assembly) 240, a rotary optical andelectromagnetic coupler including an optical inputter 102, the opticalfiber 241, a rotary transformer 211, and the probe driving unit 100 fordriving the PAE-EUS probe 200.

The two concepts of the waveguide assembly 240 that includes the opticalfiber 241, and the rotary optical and electromagnetic coupler thatincludes the optical inputter 102 and the rotary transformer 211, arerespectively applied to a flexible section, i.e., the plastic catheter220 section formed in the PAE-EUS probe 200 of FIG. 1 for insertion intothe object to be examined and having a long and slender shape; and abase portion connected to the probe driving unit 100 at a proximal part210 of the PAE-EUS probe 200.

Referring to FIG. 1, the PAE-EUS probe 200 is divided into a portionsurrounded by the plastic catheter 220 and a portion that is theproximal part 210 physically surrounded by a base frame 216. Since thesection surrounded by the plastic catheter 220 is physically flexibleand has a long and slender tubular shape, the section may be effectivelyinserted into the object to be examined that may be accessible onlythrough a narrow and curved path.

Also, since the plastic catheter 220 encloses the waveguide assembly 240and the scanning tip 250 located in an inner space of the plasticcatheter 220, and isolates the waveguide assembly 240 and the scanningtip 250 from an external space, the plastic catheter 220 prevents thewaveguide assembly 240 and the scanning tip 250 from directly contactingthe object to be examined. Also, the plastic catheter 220 may trap amatching liquid medium 230 filled in the plastic catheter 220 and mayprevent the matching liquid medium 230 from leaking out. Since a laserbeam and acoustic waves have to pass through a wall of the plasticcatheter 220, the plastic catheter 220 may be formed of an opticallytransparent polymer-based material through which both the laser beam andacoustic waves may easily pass.

Although ultrapure water, such as deionized water, may be used as thematching liquid medium 230 filled in the inner space of the plasticcatheter 220, it is preferable that a material used as the matchingliquid medium 230 may be bio-friendly and may be usablesemi-permanently, such as silicone oil (polydimethylsiloxane: PDMS) witha low viscosity and a high optical clarity. When water is used for thematching liquid medium 230, it is important to surely electricallyinsulate two conductive paths (which will be explained below) of thewaveguide assembly 240 immersed in the matching liquid medium 230.

Since the plastic catheter 220 has a long and slender tubular shape, theplastic catheter 220 may be effectively inserted into the object to beexamined that may be accessible only through a narrow and curved path.Accordingly, the plastic catheter 220 may be formed to have a diameterequal to or greater than about 1 mm and equal to or less than about 3mm, and a total length equal to or greater than about 0.5 m and equal toor less than about 3 m.

The waveguide assembly 240 is located in the inner space of the plasticcatheter 220 and extends from the proximal part 210 to the scanning tip250. The waveguide assembly 240 is also physically flexible and deliversa photoacoustic signal and an ultrasonic signal detected by apiezoelectric element 251.

The scanning tip 250 is located at one end of the waveguide assembly240. The scanning tip 250 delivers a laser beam guided through theoptical fiber 241 in the waveguide assembly 240 or an ultrasonic pulsegenerated by the piezoelectric element 251 to the object to be examined,and also detects a photoacoustic signal generated in the object to beexamined or an ultrasonic signal reflected from the object to beexamined. The scanning tip 250 may include an optical reflector 252 thatreflects a laser beam guided through the optical fiber 241 in thewaveguide assembly 240 to a target point, the piezoelectric element 251that generates a very short ultrasonic pulse or detects an ultrasonicsignal or a photoacoustic signal generated from the object to beexamined, a sound-absorbing backing layer 253 that may remove noisegenerated due to irregular reflection of sound waves, and a metal casing254 that surrounds the piezoelectric element 251, the optical reflector252, and the sound-absorbing backing layer 253.

The proximal part 210 that is connected to the waveguide assembly 240and receives mechanical torque from the probe driving unit 100 andtransmits the mechanical torque to the waveguide assembly 240 is locatedat the other end of the waveguide assembly 240. The proximal part 210may include a proximal gear 217, the rotary transformer 211, a ballbearing module 212, a sealing O-ring 213, a hollowed shaft 214, an epoxyfiller 215, and the base frame 216 that surrounds the rotary transformer211, the ball bearing module 212, the sealing O-ring 213, the hollowedshaft 214, the epoxy filler 215, and the proximal gear 217.

The proximal gear 217 receives mechanical torque from the probe drivingunit 100 and transmits the mechanical torque to the waveguide assembly240. The rotary transformer 211 is located in the proximal part 210 andreceives an electrical pulse generated from an ultrasonicpulser-receiver 101 and transmits the electrical pulse to thepiezoelectric element 251 or receives an electrical signal generatedfrom the piezoelectric element 251 and transmits the electrical signalto the ultrasonic pulser-receiver 101. Any electrical signal in the twoprocesses passes through the waveguide assembly 240.

The sealing O-ring 213 prevents the matching liquid medium 230 filledinside the plastic catheter 220 from leaking out. The ball bearingmodule 212 provides a mechanical condition in which the hollowed shaft214 may smoothly rotate at a stable position.

The probe driving unit 100 is a physically independent unit that may beseparated from the PAE-EUS probe 200. The probe driving unit 100 mayinclude the ultrasonic pulser-receiver 101 that may transmit or receivean electrical signal to or from the rotary transformer 211 and mayamplify a received electrical signal; the optical inputter 102 thatinputs a laser pulse to the optical fiber 241 that rotates, byconstituting a rotary optical coupler along with the optical fiber 241;a driving gear 103 that transmits mechanical torque to the waveguideassembly 240; an actuator 104 coupled to the driving gear 103; and anactuator driver 105 that controls the actuator 104, which will beexplained below.

The elements illustrated in FIG. 1 are just essential elements needed toexplain the major result derived from the present disclosure, and systemelements that are obviously required according to common sense may beadded if necessary. For example, the metal casing 254 may be formed withmultiple pieces rather than a single piece of metal.

The optical fiber 241 and the conductive path CP included in thewaveguide assembly 240 will now be explained.

FIG. 2 is a cross-sectional view taken along line II-II′ of FIG. 1.

Referring to FIG. 2, the optical fiber 241 generally includes a core anda cladding, and may include a protective coating layer 241 PCL formed ofa polymer or the like outside the core and the cladding. The conductivepath CP that is coaxially arranged with the optical fiber 241, surroundsthe optical fiber 241, and delivers an electrical signal, is locatedoutside the optical fiber 241. The conductive path CP includes the firstconductive path 242 including a portion coaxially arranged with theoptical fiber 241, and the second conductive path 243 including aportion coaxially arranged with the optical fiber 241 and insulated fromthe first conductive path 242.

The key feature of the present disclosure is that the optical fiber 241,the first conductive path 242, and the second conductive path 243 areall coaxially arranged along one reference point, i.e., the central axisof the waveguide assembly 240, and rotate together as an integrativeunit at the same angular speed during the rotation, which will beexplained below.

According to an embodiment, a first conductive path 242 may surround theoptical fiber 241, and a second conductive path 243 may be coaxiallyarranged with the first conductive path 242 and may surround the firstconductive path 242. That is, cross-sections of the optical fiber 241,the first conductive path 242, and the second conductive path 243 mayhave concentric circular shapes as shown in FIG. 2. In this case, atleast one of the first conductive path 242 and the second conductivepath 243 may have a tubular shape. When at least one of the firstconductive path 242 and the second conductive path 243 has a tubularshape, the first conductive path 242 and/or the second conductive path243 has a hollowed tubular shape with a predetermined thickness andsurrounds an outer surface of the optical fiber 241. In this case, atleast one of the first conductive path 242 and the second conductivepath 243 may be formed by directly coating a conductive material on theouter surface of the optical fiber 241 by using, for example, sputteringor vapor deposition.

In order to insulate the first and second conductive paths 242 and 243,a surface of each of the first and second conductive paths 242 and 243may be coated with an insulating layer IL. The insulating layer IL mayinclude a polymer. Alternatively, a tubular structure made of aninsulating material may be additionally inserted between the first andsecond conductive paths 242 and 243.

Referring back to FIGS. 1 and 2, the optical fiber 241 is located at thecenter of the waveguide assembly 240, and the first conductive path 242and the second conductive path 243 are coaxially arranged outside theoptical fiber 241. In this particular structure, the optical fiber 241located at the center functions as an optical waveguide that deliverslaser light, and the first and second conductive paths 242 and 243function as an electromagnetic waveguide that may deliver a highfrequency electrical signal (typically in a radio frequency (RF) range)very effectively, like the electric coaxial cables that are commonlyutilized in many RF devices. For reference, the typical frequency of anelectrical signal used herein may range from about 0.1 MHz to about 100MHz, and the optical fiber 241 used herein may be a multi-mode opticalfiber, a single-mode optical fiber, or a combination thereof, accordingto a desired purpose of an application.

In addition to functioning as an optical and electromagnetic waveguide,the waveguide assembly 240 may also function as a flexible shaft thattransmits mechanical torque from the proximal part 210 to the scanningtip 250, when the optical fiber 241, the first conductive path 242, andthe second conductive path 243 are effectively formed as an integratedsingle unit of mechanical components, which is another important featuredifferent from the prior arts. Accordingly, the first conductive path242 and the second conductive path 243 have to have shapes or structuresthat may be easily bent. If there is a physical interval or gap betweenthe optical fiber 241 and the first and second conductive paths 242 and243, for example, the waveguide assembly 240 may be more flexibly bentand effectively transmit mechanical torque.

In short, the present disclosure is characterized by the unique systemfeature that a waveguide assembly 240 capable of transmitting not onlylaser light and an electrical signal but also a very uniform mechanicaltorque based on the rotationally symmetric structure is employed in aPAE-EUS system that operates based on a single-element ultrasonictransducer-based proximal actuation mechanism.

FIG. 3 is a view illustrating a configuration of a coaxially configuredoptical and electromagnetic rotary waveguide assembly in aphotoacoustic-ultrasonic endoscope, according to another embodiment.FIG. 4 is a perspective view illustrating a detailed configuration of aportion A of FIG. 3. FIG. 5 is a photo showing a real embodiment of thewaveguide assembly 240 according to the structure shown in FIG. 4. Inparticular, FIG. 3 illustrates how the waveguide assembly 240 accordingto this specific embodiment is installed and electrically connected inthe PAE-EUS probe 200.

As described above, the waveguide assembly 240 includes the opticalfiber 241 that may deliver light, and the conductive path CP including afirst conductive path including a portion coaxially arranged with theoptical fiber 241 and a second conductive path including a portioncoaxially arranged with the optical fiber 241 and insulated from thefirst conductive path 242.

According to an embodiment, the first conductive path 244 may surroundthe optical fiber 241, the second conductive path 245 may be coaxiallyarranged with the first conductive path 244 and may surround the firstconductive path 244, and at least one of the first conductive path 244and the second conductive path 245 may include a torque coil set formedas a coil and located outside the optical fiber 241.

Referring to FIG. 4, the first conductive path 244 and the secondconductive path 245, which surround the optical fiber 241, may includetorque coil sets 244 and 245. Here, the torque coil sets 244 and 245 arerespectively referred to as an inner torque coil set 244 and an outertorque coil set 245. The reason that the term “set” is attached to eachname is because each torque coil may have a single-layered structure asshown in FIG. 4 or a multi-layered structure in which multi-layeredtorque coils overlap and function as one unit. For example, referring toFIG. 5, each torque coil set 244 or 245 may have a two-layered structurecomposed of a plurality of wires (see the cross-sectional view). Thisstructure may, in general, more effectively transmit mechanical torqueover a very long probe section greater than 1 m. When a given space islimited and the flexibility of a probe is relatively more important,each torque coil set 244 or 245 may have a single-layered structure asshown in FIG. 4.

In order to increase the electrical conductivity of each of the innerand outer torque coil sets 244 and 245, the surface of each of the innerand outer torque coil sets 244 and 245 may be coated or plated with amaterial that has high electrical conductivity, if necessary.Alternatively, the entire bodies of the torque coil sets 244 and 245 maybe fabricated with a single material that has high electricalconductivity. In either case, in order to electrically insulate theinner and outer torque coil sets 244 and 245, the outermost surface ofeach of the inner and outer torque coil sets 244 and 245 may be coatedwith a polymer-based insulating material, or a thin-wall tube 244PT (seeFIG. 5) formed of a polymer may be inserted between the inner and outertorque coil sets 244 and 245. Any of these two methods may be used in anembodiment.

Although a method of implementing the waveguide assembly 240 by usingtorque coil sets has been described with reference to FIG. 5, thewaveguide assembly 240 may be implemented by applying a method ofinserting and overlapping two conductive tubes each having a small wallthickness, instead of using torque coils.

Referring back to FIG. 3, the inner torque coil set 244 functioning as afirst conductive path and the outer torque coil set 245 functioning as asecond conductive path are respectively connected to the two electrodesof the piezoelectric element 251 and provide a path through which anelectric current flows from the scanning tip 250 to the rotarytransformer 211 located in the proximal part 210. The inner and outertorque coil sets 244 and 245 included in the waveguide assembly 240 arealso electrically connected to a primary coil unit 211-1, which is aleft coil unit, of the rotary transformer 211 that rotates along withthe inner and outer torque coil sets 244 and 245.

FIGS. 6 and 7 show a perspective view and a cross-sectional viewillustrating a configuration of the coaxially configured optical andelectromagnetic rotary waveguide assembly according to respectiveembodiments.

Referring to an embodiment of FIG. 6, a first conductive path 248 and asecond conductive path 249 may surround at least a portion of theoptical fiber 241. Referring to a cross-sectional view of the waveguideassembly 240 of FIG. 6 taken along line VI-VI′, the conductive path CPis divided into the first conductive path 248 having a U shape and thesecond conductive path 249 having an inverted-U shape. Each of the firstand second conductive paths 248 and 249 surrounds a part of the opticalfiber 241. In this case, since the first conductive path 248 and thesecond conductive path 249 of the conductive path CP are geometricallycoaxial with the optical fiber 241 and provide a path through which anelectric current flows, even when the waveguide assembly 240 is bent,the conductive path CP may transmit mechanical torque very uniformly. Aninsulating coating layer 246 that prevents electricity leakage due tocontact with the matching liquid medium 230 may be formed on an outersurface of the conductive path CP.

Referring to FIG. 7, the waveguide assembly 240 according to anembodiment may include the insulating coating layer 246 located betweenthe first conductive path 242 (that is, an inner conductive layer) and asecond conductive path 247. That is, the waveguide assembly 240 may beconfigured so that the first conductive path 242 surrounding the entiresurface of the cladding 241Cd of the optical fiber 241 and having atubular shape, the insulating coating layer 246 surrounding the entireouter surface of the first conductive path 242, and the secondconductive path 247 embodied with a torque coil set are sequentiallylocated from inside to outside in this stated order. In this case, theinsulating coating layer 246 electrically insulates the first and secondconductive paths 242 and 247. In this embodiment, the first conductivepath 242 may be directly coated on the entire surface of the cladding241Cd of the optical fiber 241.

A structure of FIGS. 6 and 7 may be more effectively applied to anintravascular imaging endoscope in which an overall diameter of a probehas to be very small.

FIG. 8 shows a perspective view and a cross-sectional view of thecoaxially configured optical and electromagnetic rotary waveguideassembly including a double-clad optical fiber, according to anembodiment.

According to this embodiment, the optical fiber 241 of the waveguideassembly 240 may include not only the core 241Co and a first cladding241Cd-1 that surrounds the core 241Co and may deliver light but also asecond cladding 241Cd-2 that surrounds the first cladding 241Cd-1.

In FIG. 1, the waveguide assembly 240 selectively uses a multi-modeoptical fiber or a single-mode optical fiber. In general, the multi-modeoptical fiber has advantages in that the multi-mode optical fiber maytransmit a large amount of light energy. On the other hand, although thetotal energy delivered by the single-mode optical fiber is small, thesingle-mode optical fiber has advantages in that the single-mode opticalfiber may be able to more easily focus laser light in conjunction with alens or the like mounted at the distal end of the optical fiber. When alarge amount of light energy needs to be delivered and the light needsto be focused as well, the waveguide assembly 240 may include theoptical fiber 241 with a double cladding structure as shown in FIG. 8.In the optical fiber 241 with a double cladding structure, as shown in across-sectional view of the waveguide assembly 240 of FIG. 8 taken alongline VIII-VIII′, the core 241Co that may deliver single-mode opticalwaves is located at the center and the first cladding 241Cd-1 that maydeliver multi-mode optical waves is located outside the core 241Co andsurrounds the core 241Co. In this case, the second cladding 241Cd-2 islocated at the outermost position so that the first cladding 241Cd-1functions as an optical fiber that may also propagate light.

When the optical fiber 241 and the first and second conductive paths 244and 245 of the conductive path CP are coaxially arranged as describedabove, the mechanical torque applied to the proximal part 210 may beuniformly transmitted to the scanning tip 250 located at an end of thePAE-EUS probe 200.

Referring back to FIG. 1, The PAE-EUS system including the rotarytransformer 211 and the rotary optical coupler including the opticalinputter 102 and the optical fiber 241 will now be explained. Forreference, the rotary transformer 211 and the rotary optical couplerincluding the optical inputter 102 and the optical fiber 241 arecollectively referred to as a rotary optical and electromagneticcoupler, i.e., a unit including the rotary transformer 211, the opticalinputter 102, and the optical fiber 241.

The PAE-EUS system according to an embodiment includes the PAE-EUS probe200 and the probe driving unit 100. The PAE-EUS probe 200 includes thewaveguide assembly 240 including the optical fiber 241, including thecore 241Co (see FIG. 7) and the cladding 241Cd (see FIG. 7), and theconductive path CP, coaxially arranged with the optical fiber 241, thescanning tip 250 located at an end of the waveguide assembly 240 andconfigured to deliver a laser beam to the object to be examined anddetect a photoacoustic signal and an ultrasonic signal generated fromthe object to be examined, the plastic catheter 220 surrounding outersurfaces of the waveguide assembly 240 and the scanning tip 250, and therotary transformer 211 electrically connected to the conductive path CP.The probe driving unit 100 includes the optical inputter 102 thatdelivers light energy to the optical fiber 241 which rotates and theultrasonic pulser-receiver 101 that is electrically connected to therotary transformer 211.

The rotary transformer 211 refers to an electric element in which theprimary coil unit 211-1 in which an electric wire wound along an inneror side edge of a magnetic core with a ring shape to be parallel to themagnetic core forms one group, and the secondary coil unit 211-2 inwhich another electric wire with the same structure as that of theelectric wire of the primary coil unit 211-1 forms another group, thetwo groups facing each other so as to be symmetric with each other.

The primary coil unit 211-1 is electrically connected to the conductivepath CP of the waveguide assembly 240 and the secondary coil unit 211-2is electrically connected to an output/input port (not shown) of theultrasonic pulser-receiver 101. Accordingly, when the proximal gear 217starts to rotate and thus even the waveguide assembly 240, the hollowedshaft 214 connected to the waveguide assembly 240, and the primary coilunit 211-1 with a ring shape formed around the hollowed shaft 214 alsorotate together, the base frame 216 and the secondary coil unit 211-2 donot rotate due to the ball bearing module 212. That is, unlike theprimary coil unit 211-1 electrically connected to the first and secondconductive paths 242 and 243 of the waveguide assembly 240, thesecondary coil unit 211-2 is fixed to the base frame 216 and does notrotate. As a result, an electrical signal may be input/output to/fromthe rotating waveguide assembly 240 without the problem in which anypair of electric wires are intertwined.

That is, the rotary transformer 211 is a key electrical element thatoperates based on the electromagnetic induction principle and maytransmit/receive an electrical signal without any direct physicalcontact between two relatively moving objects or through wires. Althoughthe rotary transformer 211 has limitations in that the rotarytransformer 211 may deliver only an alternating current (AC) signal dueto the electromagnetic induction principle, the rotary transformer 211has key advantages in that the rotary transformer 211 maytransmit/receive an electrical signal to/from a rotating body withoutdirect physical contact with the rotating body. Also, by appropriatelyselecting the winding turns ratio between the electric wires of the twogroups, the rotary transformer 211 may change a voltage or electricalimpedance when delivering an electrical signal. Regarding the positionof the rotary transformer 211, it may be switched with the ball bearingmodule 212 or the proximal gear 217.

The optical inputter 102 that is, for example, a convex lens or anobjective lens, inputs laser light into the optical fiber 241 thatrotates. That is, when a laser pulse is generated by a light source 300(see FIG. 13), the laser pulse propagates through a separate guidingoptical fiber (not shown) to the optical inputter 102. In this case, theoptical inputter 102 delivers the guided laser pulse to the opticalfiber 241 placed along the central axis of the waveguide assembly 240.The important feature is that the optical fiber 241 of the waveguideassembly 240 rotates whereas the optical inputter 102 delivers laserlight in a static condition, i.e., without any physical rotation. Thatis, the optical inputter 102 that inputs laser light and the opticalfiber 241 that receives the laser light constitute a virtually pairedunit, called “rotary optical coupler”.

If necessary, instead of the optical inputter 102, such as a convex lensor an objective lens, shown in FIG. 1, a rotary optical coupler may beformed to have an alternative configuration in which the guiding opticalfiber (not shown) is directly engaged with the optical fiber 241 of thewaveguide assembly 240. In this case, the end of the guiding opticalfiber has to be positioned as close to the optical fiber 241 of thewaveguide assembly 240 as possible. Also, it is preferable that opticalfibers with the same specifications are used for the guiding opticalfiber and the optical fiber 241 of the waveguide assembly 240 so thatlight energy may be more effectively delivered through the junction.

The ultrasonic pulser-receiver 101 is electrically connected to therotary transformer 211 and receives a photoacoustic signal and anultrasonic signal detected or electrically converted by thepiezoelectric element 251, which will be explained below.

FIGS. 9 through 11 are views each illustrating a variation of thePAE-EUS probe 200 from the basic configuration shown in FIG. 1,according to an embodiment.

FIG. 9 is a view illustrating a structure and a configuration of ametal-mesh embedded plastic catheter according to an embodiment.

According to an embodiment, the PAE-EUS system may further include areinforcement 260 located inside the plastic catheter 220. Referring toFIG. 9, the reinforcement 260 is a braided or mesh reinforcement made ofa metal material that may be embedded into the plastic catheter 220.Accordingly, a lifetime of the plastic catheter 220 may be extended.

FIG. 10 is a view for explaining a shape and a structure of the plasticcatheter modified to be used for intravascular endoscopy, and a methodof injecting a liquid medium, according to an embodiment.

Referring to an embodiment of FIG. 10, the base frame 216 may furtherinclude an injection port 261. When the PAE-EUS probe 200 of the presentdisclosure is to be used by a method in which the probe is not insertedinto the instrument channel of a video endoscope currently used inclinics, an outlet port 262 may be formed by opening an end portion ofthe plastic catheter 220, the injection port 261 may be additionallyprovided in the base frame 216, and the PAE-EUS probe 200 may be usedfor the diagnosis of intravascular diseases, like an existing IVUScatheter probe. In this case, the liquid medium injected through theinjection port 261 may be a saline solution; then, the matching liquidmedium 230 filled in an inner space of the PAE-EUS probe 200 will be thesame saline solution.

FIG. 11 is a view for explaining a configuration of the plastic catheterto be used with a guiding wire, and a process of performing pullbackscanning, according to an embodiment.

Referring to FIG. 11, the PAE-EUS system may further include a guidingcatheter 290 that surrounds the plastic catheter 220 and includes aguiding catheter injection port 280, and thus may be capable ofoperating with a guiding wire 270 manufactured as a separate device tobe inserted into the guiding catheter injection port 280.

That is, when the guiding catheter 290 which has a dual-lumenalstructure over a partial section of the catheter is additionally used asshown in FIG. 11, a liquid medium may be injected through the guidingcatheter injection port 280 and also a channel through which the guidingwire 270 may be inserted and guided may be secured. Since the diameterof the plastic catheter 220 is narrower than that of the guidingcatheter 290 and the plastic catheter 220 may be physically inserted orretracted, a 3D image may be obtained by changing the position of thescanning tip 250 inside the object to be examined.

FIG. 12 is a view for explaining a method of transmitting mechanicalpower and inputting/outputting an electrical signal, which is differentfrom that in FIG. 1, in the probe driving unit 100 and the proximal part210, according to an embodiment.

In the PAE-EUS system of FIG. 1, the probe driving unit 100 includes thedriving gear 103 that is connected to the actuator 104 and rotates, andthe proximal part 210 includes the proximal gear 217 that is engagedwith the driving gear 103 and rotates following it. That is, themechanical torque needed to rotate the waveguide assembly 240 istransmitted by the proximal gear 217 directly coupled to the drivinggear 103.

However, in the PAE-EUS system of FIG. 12, the probe driving unit 100may include a driving timing pulley 106 that is connected to theactuator 104 and rotates, and the proximal part 210 may include aproximal timing pulley 218 that is engaged with the driving timingpulley 106 and rotates and may further include a timing belt 107 thattransmits the mechanical torque between the driving timing pulley 106and the proximal timing pulley 218. Accordingly, in this case, themechanical torque needed to rotate the waveguide assembly 240 istransmitted through the driving timing pulley 106, the proximal timingpulley 218, and the timing belt 107 that connects the driving timingpulley 106 and the proximal timing pulley 218.

Also, in FIGS. 1 and 3, a rotary transformer 211 is mounted in theproximal part 210 and receives an electrical signal generated by thepiezoelectric element 251 through the waveguide assembly 240. However,when mechanical noise is not a major part of consideration, the rotarytransformer 211 may be replaced with the electrical signal input/outputmethod that uses two slip rings 219-1 and two brushes 219-2 respectivelycontacting the slip rings 219-1 as shown in FIG. 12. In this case, thetwo brushes 219-2 are electrically connected to the ultrasonicpulser-receiver 101 through signal cables 219-3.

Although both the proximal timing pulley 218 and the slip rings 219-1are used in FIG. 12, the proximal timing pulley 218-based torquetransmission mechanism may be used along with the concept of rotarytransformer 211, or the proximal gear 217-based torque transmissionmechanism may be used along with the concept of slip rings 219-1.

While configurations of the PAE-EUS probe 200 and the probe driving unit100 have been described above, in order to actually performphotoacoustic and ultrasonic dual-mode endoscopic imaging by using thePAE-EUS probe 200 and the probe driving unit 100, other elements such asa light source or a data acquisition (DAQ) system are additionallyrequired, like well-known or general PAT systems.

FIG. 13 is a conceptual diagram illustrating the PAE-EUS probe 200, theprobe driving unit 100, and peripheral systems for driving the PAE-EUSprobe 200 and the probe driving unit 100. Representative examples of theperipheral systems include the light source 300 that generates a laserpulse and a system console 400 with which a user may control the entiresystem.

First, it is preferable that an essential element of the light source300 is the Q-switched laser system that may be able to provide a laserbeam with a very short pulse width. Also, sufficient pulse energy and asufficient pulse repetition rate should be ensured by the Q-switchedlaser system to satisfy the purpose of an application required by theendoscopic system. When multi-wavelength photoacoustic imaging is to besimultaneously performed at two or more wavelengths, a plurality oflaser systems capable of providing the two or more wavelengths, or awavelength tunable laser system, may be used.

The system console 400 includes a data acquisition system 402 thatreceives a photoacoustic signal and an ultrasonic signal amplified andoptimized by the ultrasonic pulser-receiver 101 and converts thephotoacoustic and ultrasonic signal into a digital signal that may bemanaged by a computer, a data processor 401 that processes the digitalsignal into image data, an image displayer 403 that shows the image datato the user, and a subsystem controller 404 that controls a plurality ofsub-systems.

Operations of the PAE-EUS probe 200 and the probe driving unit 100 ofFIG. 1 will now be explained with reference to FIGS. 1 and 13.

The user inserts the PAE-EUS probe 200 into the object to be examined sothat the scanning tip 250 is located in a region of interest, drives theactuator 104 so that the driving gear 103 and the proximal gear 217engaged with the driving gear 103 start to rotate and accelerate toreach a predetermined speed. For example, when imaging is to beperformed at a general video rate, the proximal gear 217 may beaccelerated to about 30 Hz.

Once the proximal gear 217 starts to rotate, the hollowed shaft 214directly connected to the proximal gear 217 also rotates. In this case,the mechanical torque is also directly transmitted to the primary coilunit 211-1 of the rotary transformer 211 engaged with the hollowed shaft214, the waveguide assembly 240, and the scanning tip 215 located at anend portion of the waveguide assembly 240, and thus the primary coilunit 211-1, the waveguide assembly 240, and the scanning tip 215 alsorotate at a predetermined speed. In this case, the ball bearing module212 of the proximal part 210 provides a mechanical condition in whichthe hollowed shaft 214 may smoothly rotate in a stable state, and thesealing O-ring 213 prevents the matching liquid medium 230 filled in aninner space of the PAE-EUS probe 200 from leaking out during thephysical rotation.

When the mechanical elements interconnected with one another reach thepredetermined speed, the actuator driver 105 starts to generate atrigger pulse signal whenever the actuator 104 which is actually themechanical power source rotates by a predetermined angular step, and aseries of imaging sequences for obtaining one-dimensional (1D)photoacoustic and ultrasonic image data (typically, referred to asA-line data) in synchronization with the trigger pulse signal aresequentially and alternately performed in the entire system. That is,every time a trigger pulse signal is generated, 1D photoacoustic andultrasonic data containing depth-resolved information (i.e.,radially-resolved information) in a specific direction in which thescanning tip 250 faces is obtained, and pieces of 2D photoacoustic andultrasonic image data that are spatially coregistered are obtained bycontinuously and repeatedly performing such a series of processes whilethe scanning tip 250 rotates. Also, when the series of processes areperformed by pushing or pulling the PAE-EUS probe 200, the data neededfor producing a 3D image may also be obtained. A trigger pulse used totrigger the imaging sequences may be a transistor-transistor logic (TTL)pulse.

In order to sequentially obtain pieces of 1D photoacoustic andultrasonic data by using the above method, a trigger pulse trainprovided by the actuator driver 105 is delivered to the subsystemcontroller 404, is divided into two different pulse trains with apredetermined time interval therebetween in the subsystem controller404, and is used for photoacoustic and ultrasonic imaging. Thepredetermined time interval may be tens of micro seconds (μsec) ingeneral. The reason that 1D photoacoustic and ultrasonic dataacquisition moments are triggered separately with a set time interval isbecause the object to be examined is given time to sufficiently relax inthe two photoacoustic and ultrasonic modes that alternately occur. Forreference, the prior document 11 discloses that such imaging sequencesare actually used.

How 1D photoacoustic and ultrasonic image data are obtained by using asingle trigger pulse will now be explained.

First, when a photoacoustic imaging mode for obtaining 1D photoacousticdata starts at a specific time, a laser pulse is first generated by thelight source 300, the laser pulse is sent through a separate opticalfiber (not shown) to the optical inputter 102, is delivered along theoptical fiber 241 provided along the central axis of the waveguideassembly 240 from the proximal part 210 to the scanning tip 250, and isfinally sent through the optical reflector 252 to the object to beexamined. When the light source 300 is integrated with the probe drivingunit 100, a separate optical fiber for delivering a laser pulsegenerated by the light source 300 to the probe driving unit 100 is notrequired.

When a laser beam is delivered into the object to be examined,photoacoustic waves are immediately induced, and a part of the inducedphotoacoustic waves propagate to the piezoelectric element 251 and theyare converted into an electrical signal. The electrical signal is guidedthrough the electromagnetic waveguide formed by the first conductivepath 242 and the second conductive path 243 of the waveguide assembly240 and through the rotary transformer 211 of the proximal part 210 tothe ultrasonic pulser-receiver 101 of the probe driving unit 100.Although the ultrasonic pulser-receiver 101 receives a photoacousticsignal detected and electrically converted by the piezoelectric element251, the ultrasonic pulser-receiver 101 may also provide an electricalpulse to the piezoelectric element 251 so that the piezoelectric element251 emits an ultrasonic pulse to the object to be examined, and mayreceive the ultrasonic echo signal detected by the piezoelectric element251.

In addition, the ultrasonic pulser-receiver 101 may perform a signalconditioning to amplify a signal and filter only an appropriatefrequency band. Optimized signals are then sent to the data acquisitionsystem 402, are processed by the data processor 401 of the systemconsole 400, and are stored temporarily or for a long time.

When a series of processes of obtaining 1D photoacoustic data end, anultrasonic imaging mode for obtaining 1D ultrasonic data with a presettime interval starts. The scanning tip 250 may rotate a little duringthe preset time interval.

When this process starts, a very short electrical pulse is generated inthe ultrasonic pulser-receiver 101, is delivered through the rotarytransformer 211 and the first conductive path 242 and the secondconductive path 243 of the waveguide assembly 240 to the piezoelectricelement 251, and is converted into an ultrasonic pulse. The ultrasonicpulse propagates to the object to be examined in a similar manner tothat in a typical ultrasonic imaging process, a part of the ultrasonicpulse is reflected and returned and is detected by the samepiezoelectric element 251 that has emitted the ultrasonic pulse, and thereceived part of the ultrasonic pulse is converted into an electricalsignal. Next, the electrical signal is further delivered through thefirst conductive path 242 and the second conductive path 243 of thewaveguide assembly 240 to the rotary transformer 211 and is finallyreceived and amplified by the ultrasonic pulser-receiver 101 in reverseorder. The amplified ultrasonic signal is sent to the data acquisitionsystem 402, is processed by the data processor 401 of the system console400, and is stored temporarily or for a long time, like thephotoacoustic signal.

Once 1D photoacoustic and ultrasonic image data are obtained accordingto the above method for a predetermined time (e.g., while the scanningtip 250 completely rotates one time, in general), pieces of related dataare processed by the data processor 401 and are displayed to the userthrough the image displayer 403.

The main objective of the present disclosure is for it to be used in aphotoacoustic and ultrasonic dual imaging mode. But, if the opticalfiber 241 of the waveguide assembly 240 is an optical fiber having adouble cladding structure or a single-mode optical fiber, and alsoperipheral systems elements are configured as shown in FIG. 14, aphotoacoustic-ultrasonic-OCT triple imaging mode may also be performed.

FIG. 14 is a conceptual diagram illustrating system elements forimplementing a photoacoustic-ultrasonic-OCT triple imaging mode, and aconnection relationship among the system elements.

Referring to FIG. 14, a photoacoustic-ultrasonic-OCT imaging systemaccording to an embodiment includes an OCT light source 302 forproviding optical waves for OCT imaging to the optical fiber 241. Abiggest difference between FIGS. 13 and 14 is internal configurations ofthe light source 300 and the probe driving unit 100. First, the OCTlight source 302, e.g., a swept source, is added to the light source 300in order to perform OCT. For reference, the term ‘added’ means theaddition of a function and it does not mean that a physically separateunit or apparatus has to be added. For example, a single light sourcemay simultaneously provide the optical waves needed for photoacousticimaging and OCT imaging. In FIG. 14, besides the OCT light source 302,an optical interferometer/optical signal detector 108 that is typicallyused in an OCT imaging system may be provided in the probe driving unit100, may receive optical waves from the OCT light source 302, and mayadditionally perform OCT imaging. In order to effectively deliver thelaser light received from the photoacoustic light source 301 and theoptical waves received from the OCT light source 302 to the PAE-EUSprobe 200, a beam combiner 109 may also be provided in front of theoptical inputter 102.

The photoacoustic-ultrasonic-OCT images that are spatially coregisteredmay be obtained by sequentially starting 1D photoacoustic, ultrasonic,and OCT imaging modes while the scanning tip 250 rotates in a mannersimilar to that described above.

A method of obtaining photoacoustic, ultrasonic, and OCT imageinformation by using the endoscopic system of the present disclosure hasbeen described. However, if necessary, a system for obtaining only someof image information from among the photoacoustic, ultrasonic, and OCTimage information may be implemented. In configurations and arrangementsof detailed system elements, e.g., the probe driving unit 100, the lightsource 300, and the system console 400 of FIGS. 13 and 14, some elementsmay be integrated as one physical unit if necessary, and positions ofsub-systems in the elements may be appropriately changed. For example,the light source 300, the probe driving unit 100, and the system console400 may be integrally formed, and the OCT light source 302 may be movedto be located inside the probe driving unit 100.

The present disclosure may provide a method of solving the fastidiousproblems related to the wiring of the optical fiber 241 and anelectrical signal line, and inputting/outputting of optical waves andelectrical signals in the proximal part 210, which have been verysignificant problems in the PAE system that operates based on thesingle-element ultrasonic transducer-based proximal actuation mechanism,by using the inventive principles and structures of the waveguideassembly 240 and the rotary optical and electromagnetic couplerincluding the optical inputter 102, the optical fiber 241, and therotary transformer 211.

The key requirement of a PAE system that uses the proximalactuation-based rotation scanning mechanism is that an optical fiber fordelivering laser light and an electrical conductive path fortransmitting/receiving an electrical signal has to be formed in apredetermined rotating body (i.e., a torque coil). But, existinginventions including Prior Document 4 have problems in that, since theoptical fiber and the electrical path are simply arranged in a parallelstructure inside the torque coil, uniform mechanical torque cannot betransmitted from the proximal part to the distal end of an imagingprobe. That is, in a PAE system that uses the proximal actuation-basedrotation scanning mechanism, the flexible probe section that is insertedinto an object to be examined is a very important path through which notonly the light energy and the electrical signal but also the mechanicaltorque needed for a rotational scanning are transmitted. However, theprior inventions fail to provide a method of solving the problems.

On the other hand, the present disclosure provides a structure and aneconomical implementation method that may effectively deliver both lightenergy and an electrical signal, without using an electrical signal linethat is typically used, by using, for example, the conductive path CPincluding the first and second conductive paths 242 and 243 which areall coaxially configured.

Accordingly, when a PAE system is implemented based on the presentdisclosure, since the PAE-EUS probe 200 has a complete rotationalsymmetric structure, the PAE-EUS probe 200 may have a flexibility androtation scanning uniformity that are much better than those of similarexisting PAE probes, and thereby NURD problems are effectively solved.Also, the PAE-EUS probe 200 is hardly affected by an electromagneticinterference noise present in an external environment, and asignal-to-noise ratio is greatly increased. Accordingly, the PAE-EUSprobe 200 may be prevented from being severely twisted or kinked when aninsertion depth is large (that is, when the PAE-EUS probe 200 is long)and a curvature is large, thereby improving image quality and greatlyextending a lifetime of the PAE-EUS probe 200. The PAE-EUS probe 200 maybe more easily inserted into the instrument channel of a video endoscopecurrently used in clinics.

In the present disclosure, detailed configurations for providing theplastic catheter 220 outside a rotating body, filling the matchingliquid medium 230 inside the plastic catheter 220, and finally sealingthe plastic catheter 220 near the base frame 216, all of which howeverhave not been achieved concurrently in the prior inventions, have beenprovided for the first time. Also, a method of configuring the rotaryoptical and electromagnetic coupler including the optical inputter 102,the optical fiber 241, and the rotary transformer 211, so that anelectrical signal can be effectively exchanged via the rotarytransformer 211 as well as a laser beam via the rotary optical couplerformed in the proximal part 210, and a method of implementing aphotoacoustic-ultrasonic-OCT triple imaging based on the proposed keydesign concept are provided.

According to an embodiment of the present disclosure including anoptical fiber and a conductive path that is coaxial with the opticalfiber, since a probe has a complete rotational symmetric structure, theprobe may have a flexibility and rotation scanning uniformity that aremuch better than those of similar existing PAE probes, thereby solvingNURD problems. However, the scope of the present disclosure is notlimited by the effect.

While one or more embodiments have been described with reference to thefigures, it will be understood by those of ordinary skill in the artthat various changes in form and details may be made therein withoutdeparting from the spirit and scope of the disclosure as defined by thefollowing claims.

What is claimed is:
 1. A photoacoustic-ultrasonic endoscope comprising aprobe operatively coupleable to a probe driving unit, the probecomprising: a rotatable, optical and electromagnetic rotary waveguideassembly including: an optical fiber having a core and at least onecladding, the optical fiber defining a longitudinal axis and beingpositioned at a center of the optical and electromagnetic rotarywaveguide assembly; a first conductor defining a first conductive path,the first conductor comprising a tubular or coiled portion coaxiallyarranged with and surrounding the optical fiber; and a second conductordefining a second conductive path, the second conductor comprising atubular or coiled portion coaxially arranged with and surrounding boththe optical fiber and the first conductor, the second conductor beinginsulated from the first conductor; a scanning tip located at a distalend of the optical and electromagnetic rotary waveguide assembly andconfigured to transmit a laser beam to an object to be examined anddetect a photoacoustic signal or an ultrasonic signal received from theobject to be examined; and an outer plastic catheter positionedexteriorly of the optical and electromagnetic rotary waveguide assemblyand the scanning tip, wherein the optical fiber guides the laser beamfrom a proximal part of the optical and electromagnetic rotary waveguideassembly to the scanning tip, wherein the first conductor and the secondconductor guide an electrical signal converted from the photoacousticsignal, from the scanning tip to the proximal part of the optical andelectromagnetic rotary waveguide assembly, and at the same time, thefirst conductor and the second conductor transmit mechanical torque fromthe probe driving unit along with the optical fiber.
 2. Thephotoacoustic-ultrasonic endoscope of claim 1, wherein at least one ofthe first conductor and the second conductor comprises a torque coil setformed as a coil exteriorly of the optical fiber.
 3. Thephotoacoustic-ultrasonic endoscope of claim 1, wherein the rotarywaveguide assembly comprises an insulating coating layer between thefirst conductor and the second conductor.
 4. Thephotoacoustic-ultrasonic endoscope of claim 1, wherein the claddingcomprises a first cladding configured to propagate light waves and asecond cladding surrounding the first cladding.
 5. Thephotoacoustic-ultrasonic endoscope of claim 1, further comprising a meshreinforcement inside the plastic catheter.
 6. Thephotoacoustic-ultrasonic endoscope of claim 1, wherein the probe furthercomprises an injection port.
 7. The photoacoustic-ultrasonic endoscopeof claim 1, further comprising: a guiding catheter surrounding theplastic catheter and comprising a guiding catheter injection port; and aguiding wire inserted into the guiding catheter injection port.
 8. Thephotoacoustic-ultrasonic endoscope of claim 1, further comprising alight source for optical coherence tomography (OCT), wherein the lightsource is configured to supply light waves for OCT to the optical fiber.9. A photoacoustic-ultrasonic endoscope comprising a probe operativelycoupleable to a probe driving unit, the probe comprising; a rotatable,optical and electromagnetic rotary waveguide assembly including: anoptical fiber having a core and at least one cladding, the optical fiberdefining a longitudinal axis and being positioned at a center of theoptical and electromagnetic rotary waveguide assembly; a first conductorformed as a first torque coil and defining a first conductive path, thefirst conductor comprising a tubular portion coaxially arranged with andsurrounding the optical fiber; and a second conductor formed as a secondtorque coil and defining a second conductive path, the second conductorcomprising a tubular portion coaxially arranged with and surroundingboth the optical fiber and the first conductor, the second conductorbeing insulated from the first conductor; a scanning tip located at adistal end of the optical and electromagnetic rotary waveguide assemblyand configured to transmit a laser beam to an object to be examined anddetect a photoacoustic signal or an ultrasonic signal received from theobject to be examined; and an outer plastic catheter positionedexteriorly of the optical and electromagnetic rotary waveguide assemblyand the scanning tip, wherein the optical fiber guides the laser beamfrom a proximal part of the optical and electromagnetic rotary waveguideassembly to the scanning tip, wherein the first conductor and the secondconductor guide an electrical signal converted from the photoacousticsignal, from the scanning tip to the proximal part of the optical andelectromagnetic rotary waveguide assembly, and at the same time, thefirst conductor and the second conductor transmit mechanical torque fromthe probe driving unit along with the optical fiber.
 10. Thephotoacoustic-ultrasonic endoscope of claim 9, wherein the first torquecoil is one torque coil of a multi-layer first torque coil set, andwherein the second torque coil is one torque coil of a multi-layersecond torque coil set.
 11. The photoacoustic-ultrasonic endoscope ofclaim 9, wherein at least one of the first torque coil and the secondtorque coil is coated with a material providing electrical conductivity.12. The photoacoustic-ultrasonic endoscope of claim 1, wherein the firstconductor has a U shape in a cross-sectional view perpendicular to thelongitudinal axis to partially surround the optical fiber, and thesecond conductor has an inverted-U shape in the cross-sectional viewperpendicular to the longitudinal axis to partially surround the opticalfiber.
 13. The photoacoustic-ultrasonic endoscope of claim 9, whereinthe first conductor has a U shape in a cross-sectional viewperpendicular to the longitudinal axis to partially surround the opticalfiber, and the second conductor has an inverted-U shape in thecross-sectional view perpendicular to the longitudinal axis to partiallysurround the optical fiber.